Why can't I install third party apps

[Odd-De-Boom]

I have just bought a galaxy s7 edge running andriod marshmellow and I am unable to install ANY third party apps (tried a few), even though I've enabled it in settings. Either nothing happens when I click on the downloaded file or an advert pops up for various different apps which then directs me to app store.

 

[Golfdriver97]

Welcome to the forums. You have a Gmail account, correct? Does this happen over both your cell signal and wifi?

 

[Odd-De-Boom]

Hi and thanks for the welcome. Yes I have a Gmail account ndiyo I've had the same problem over cell and WiFi signals.

 

[B. Diddy]

Welcome to Android Central! Are you installing through Google Play Store, or some other app store? Or are you downloading apk files from some random site?